<html>
   <head>
       <meta charset="utf-8" />
       <title>改变网页背景颜色</title>
       <style>
           body{
               background-color: green;
           }
       </style>
   </head>
   <body id="bodyid">
        <input type="button" id="btn1" value="设为红色">
        <input type="button" id="btn2" value="设为黄色">
        <input type="button" id="btn3" value="设为蓝色">
        <input type="button" id="btn4" value="设为自定义色">
   </body>
   <script type="text/javascript" src="changebg.js"></script>
 </html>